Jeff,
I use 5/8" baltic birch with the eCabs mortise and tenon joinery. For small drawers I use a 1/4" prefinished American maple ply bottom. For larger drawers or drawers that are going to be holding heavier items, I use 1/2" prefinished American maple ply. I finish the 5/8" baltic birch with MLCampbell Duravar conversion varnish - 3 coats on the inside, 2 coats on the outside. Have never had a drawer problem.
When low-budget people come to me asking for all the bells and whistles and then tell me that their budget is along the lines of big box store off the shelf particle board cabinets, I refer them to a big box store.
Not many custom cabinet makers, I know of, can beat the off the shelf el-cheapo particle board stuff. But if that is what they can afford, that's fine. I won't take the time or jump through hoops to put an estimate together for them knowing they are on a very small budget. Wastes mine and their time.